Transporting passengers and cargo by air is a highly competitive business. In order to remain competitive, commercial airlines are continually striving for ways to reduce the cost and travel time associated with air transport. One method for reducing the cost of air transport is to utilize aircraft having increased passenger and/or cargo capacity. Increasing the number of passengers and/or cargo containers on a given flight can accordingly reduce the per-passenger and/or per-container costs for that flight.
As aircraft evolve to accommodate more passengers and cargo, however, a number of negative trends develop. One such trend is the tendency for the weight of the airframe to increase. Another such trend is the tendency for both the surface area and the cross-sectional area of the airframe to increase. Each of these trends tends to increase the aerodynamic drag on the aircraft. For example, increases in weight increase induced drag (i.e., drag caused by generating lift); increases in surface area increase skin friction drag (i.e., drag caused by air flowing over the exterior surfaces of the airframe); and increases in cross-sectional area increase pressure drag (i.e., drag caused by air flowing normal to the cross-section of the airframe). These increases in drag can be offset by increases in engine thrust if the aircraft is to be capable of the relatively high airspeeds required for modern air travel. Unfortunately, however, increasing engine thrust generally requires increasing fuel consumption. As a result, the ability to reduce cost by increasing passenger and/or cargo capacity is often mitigated by the resultant increase in fuel consumption.
FIGS. 1A-C illustrate a side view, top view, and fuselage cross-sectional view, respectively, of a transonic transport aircraft 100 in accordance with the prior art. The aircraft 100 includes a fuselage 102, a tail 108, swept wings 104 extending from the fuselage 102 at a wing/body junction 105, and engine nacelles 106 suspended from the swept wings 104. As is known by those of ordinary skill in the relevant art, the “area rule” holds that the longitudinal distribution of the cross-sectional area of the aircraft 100 tends to dominate the “wave” drag experienced by the aircraft 100 due to air compressibility effects at speeds above about Mach 0.85. Accordingly, to reduce the wave drag at such speeds, the fuselage 102 has a significantly narrowed or “waisted” portion adjacent to the wing/body junction 105 to offset the increase in cross-sectional area that occurs in this region because of the wings.
The configuration of the conventional high-speed transport aircraft 100 shown in FIGS. 1A-C has a number of shortcomings. One shortcoming is the overall size of the aircraft 100 resulting from the rather elongate swept wings 104 extending from the equally elongate fuselage 102. Not only does this size contribute to excessive weight (and hence drag, as discussed above), it also increases the area required to maneuver and park the aircraft 100 during ground servicing.
Another shortcoming associated with the aircraft 100 is the dispersed weight distribution resulting from such a wing/body/tail configuration. This weight distribution requires a substantial airframe to withstand the relatively high maneuver loads encountered during flight. In addition, this weight distribution creates substantial moments of inertia about the pitch, roll, and yaw axes of the aircraft 100. As a result, substantial control forces are required to control movement of the aircraft 100 about these axes, and substantial trim forces are required to trim the aircraft 100 to counteract the larger center of gravity (CG) movements often associated with such configurations. High control/trim forces and high airframe weight result in high drag, which in turn results in increased fuel consumption. In addition, high airframe weight can also result in high landing fees because, at many airports, landing fees are based on aircraft weight.
Further shortcomings of the aircraft configuration shown in FIGS. 1A-C are associated with the waisted portion of the fuselage 102 adjacent to the wing/body junction 105. Typically, the main load-carrying structure of the wings 104 extends through the fuselage 102 at the wing/body junction 105, thereby precluding the storage of cargo in this region. As a result, cargo is typically stored in the fuselage 102 in two or more cargo holds positioned fore and aft of the wing/body junction 105 in a “dumbbell” arrangement. Not only does such an arrangement further compound the unfavorable weight distribution of the aircraft 100, it also dictates multiple points of entry into the fuselage 102 for loading and unloading cargo. Accessing two separate points of entry in this manner accounts for much of the time it takes ground crews to service the aircraft 100. A further consequence of the waisted portion of the fuselage 102 adjacent to the wing/body junction 105 is the necessary reduction in passenger seats in this region. For example, as best seen in FIG. 1C, directly aft of the wing/body junction 105, the fuselage 102 can accommodate about nine passenger seats abreast. In the waisted portion of the fuselage 102 directly adjacent to the wing/body junction 105, however, the fuselage 102 can accommodate only about six passenger seats abreast. In sum, the payload capability, structural efficiency, and ground-servicing aspects of conventional high-speed aircraft configurations, such as that shown in FIGS. 1A-C, are often compromised in an effort to reduce their drag at high speeds.